⚠️ Acute hypotension is diagnosed when systemic blood pressure falls below levels sufficient to maintain organ perfusion. Traditionally invasive monitoring was used, but non-invasive methods are now preferred where possible.

📖 About Hypotension

Hypotension = systemic blood pressure below the normal range.
No strict threshold, but <90/60 mmHg is commonly considered hypotensive.

🧪 Physiology

Blood Pressure = Cardiac Output × Total Peripheral Resistance
MAP (Mean Arterial Pressure) = 2/3 Diastolic + 1/3 Systolic
Cardiac Output = Stroke Volume × Heart Rate
Target MAP for organ perfusion = ≥65 mmHg (sepsis / shock guidelines).

🚨 Causes of Hypotension

Cause	Pathophysiology & Management
💧 Dehydration	Low circulating volume → ↓ preload & CO. 🩺 Oral/IV isotonic fluids (0.9% NaCl); monitor UO & electrolytes.
🩸 Blood Loss	Haemorrhage → ↓ volume & perfusion. 🩺 Control bleed, IV fluids, group & cross-match, PRBC transfusion.
❤️ Cardiogenic Shock (MI, HF)	Pump failure → ↓ cardiac output. 🩺 O₂, cautious fluids, inotropes (dobutamine), vasopressors (noradrenaline), treat cause (PCI for MI).
🦠 Septic Shock	Vasodilation + capillary leak → ↓ SVR. 🩺 Sepsis 6: IV fluids, IV broad-spectrum antibiotics <1h, cultures, lactate, O₂, vasopressors.
🌡️ Anaphylaxis	Histamine → vasodilation, permeability, bronchospasm. 🩺 IM adrenaline 0.5 mg (1:1000), O₂, IV fluids, antihistamines, steroids, bronchodilators.
🧠 Neurogenic Shock (SCI)	Loss of sympathetic tone → vasodilation. 🩺 Fluids, vasopressors (phenylephrine/noradrenaline), spinal care.
🕹️ Endocrine (Addison’s, Hypothyroid)	Low cortisol/thyroxine → ↓ vascular tone. 🩺 IV hydrocortisone, fluids, HRT (levothyroxine).
↕️ Orthostatic Hypotension	Autonomic failure → blood pooling. 🩺 Slow posture change, stockings, ↑ fluid/salt, meds (midodrine, fludrocortisone).
💊 Drug-induced	Excess vasodilation / volume depletion. 🩺 Withhold drug, adjust dose, IV fluids.
🌀 Vasovagal Syncope	Excess vagal tone → bradycardia + vasodilation. 🩺 Supine, fluids, reassurance; rarely β-blocker or pacing if recurrent.

🩺 Clinical Features

Light-headedness, dizziness, presyncope
Syncope, blurred/darkened vision, tinnitus
Cold, clammy peripheries; tachycardia (except neurogenic)
Reduced urine output, confusion, drowsiness if severe

🔍 Investigations

Bloods: FBC, U&E, LFT, clotting, lactate
Group & cross-match if bleeding suspected
ECG, troponin, echo for cardiogenic causes
CXR, ABG, cultures (if sepsis)
Amylase, cortisol, SynACTHen if adrenal insufficiency suspected
D-dimer, CTPA if PE suspected

🛠️ Management Principles

🔄 Airway, Breathing, Circulation (ABC) approach
💧 IV fluids if hypovolaemia present
💉 Vasopressors (e.g. noradrenaline) if MAP <65 mmHg despite fluids
🩸 Blood transfusion if haemorrhage
🦠 Sepsis → IV antibiotics within 1h, source control
🌡️ Anaphylaxis → IM adrenaline first-line
🧪 Steroids in adrenal crisis / refractory septic shock

📚 References

🧑‍⚕️ Case Examples — Acute Hypotension

Case 1 (Septic shock): 🦠 A 72-year-old man with pneumonia becomes acutely hypotensive (BP 75/45), tachycardic, febrile, and confused. Lactate is 5 mmol/L. Diagnosis: Septic shock. Teaching point: Immediate IV fluids (30 mL/kg), broad-spectrum antibiotics within 1 h, and vasopressors (noradrenaline) if MAP <65 despite fluids.
Case 2 (Hypovolaemic shock — GI bleed): 💉 A 68-year-old woman presents with massive melaena, dizziness, and hypotension (BP 70/40). HR 120 bpm, pale and clammy. Diagnosis: Hypovolaemic shock secondary to upper GI haemorrhage. Teaching point: Activate major haemorrhage protocol, secure IV access, fluid resuscitation with blood products, urgent endoscopy.
Case 3 (Cardiogenic shock — MI): ❤️‍🔥 A 60-year-old man with chest pain develops hypotension (BP 80/50), pulmonary oedema, and cold peripheries. ECG: ST-elevation MI. Diagnosis: Cardiogenic shock due to acute MI. Teaching point: Give cautious IV fluids, oxygen, inotropes (dobutamine), and urgent PCI for revascularisation.
Case 4 (Anaphylaxis): 🚨 A 35-year-old woman collapses with hypotension (BP 65/40), wheeze, urticaria, and lip swelling after eating shellfish. Diagnosis: Anaphylactic shock. Teaching point: Immediate IM adrenaline, high-flow oxygen, IV fluids; repeat adrenaline every 5 min if needed. Observe for biphasic reaction.
Case 5 (Adrenal crisis): 🧬 A 55-year-old man with Addison’s disease presents with vomiting, diarrhoea, confusion, and BP 70/45 after missing steroid tablets. He is hyponatraemic and hyperkalaemic. Diagnosis: Acute adrenal crisis. Teaching point: Immediate IV hydrocortisone 100 mg, rapid IV saline infusion, monitor glucose and electrolytes, and treat precipitating illness.

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Acute Hypotension